A hitherto-known image forming apparatus has an organic photo conductor (OPC) drum and a columnar rotating body. Such an image forming apparatus is used as a laser printer, an LED printer, a printer analogous to these printers, a facsimile machine, or a multifunctional document processor including a printer function.
As shown in FIG. 68, in such an image forming apparatus, a process cartridge 2 is removably attached to a main body, wherein the cartridge 2 has electrifying means, developing means or cleaning means, and an OPC-type photosensitive drum (hereinbelow referred to as an “OPC drum”). The image forming apparatus is further equipped with a rotating part that functions as a power transmission mechanism for rotating the OPC drum in the process cartridge 2 by means of power output from a drive source of the main body when the process cartridge 2 is loaded into the main body.
The rotating part is made up of a drive shaft that rotates integrally along with the drive source of the main body and a drum shaft for rotating the OPC drum. Indentations (female parts) and protrusions or projections (male parts) are formed in each of the drive shaft and the drum shaft. The indentations and the projections are engaged with each other, whereby drive force (rotating force) is transmitted from the drive shaft to the drum shaft.
The indentations and the projections are formed so as to assume a polygonal shape, like a triangular shape and a hexagonal shape, in order to hinder loading of an incompatible process cartridge.